The bulk material sinks downward in the chute due to gravity with a velocity which is controlled by how much bulk material is continuously removed at the bottom end of the chute.
On its way from the top to the bottom, the bulk material runs between a plurality of approximately horizontal and mostly parallel so-called air roofs, which are disposed in horizontal planes and which cover the chute from one lateral wall to the other lateral wall and which comprise an open bottom like a roof. The bulk material is thereby divided into particular flows running next to one another.
In addition, one of the faces of each roof is open, so that air can get into the roof through said open side, and can thus be blown into the chute or sucked into the chute, wherein the air is dry and mostly heated. Said roofs are called air intake roofs.
The other roofs, the so-called air exhaust roofs, on the other hand, are connected with their open face to an air exhaust duct, the so-called air exhaust plenum, so that the air which is enriched with moisture from the material to be dried and also the typically cooled down exhaust air can be exhausted. Thus, the air absorbs moisture from the drying material on its way from an air intake roof to an air exhaust roof in a transversal direction through the drying material.
Typically in top view of a drying chute, all air intake roofs are connected by an air intake plenum, which extends on one side of the drying chute over the entire height or over a partial portion of the height in vertical direction from the bottom to the top, and all air exhaust roofs are connected by an air exhaust plenum, which is disposed on the opposite side of the chute, and which also extends in vertical direction from the bottom to the top.
Since in particular the disposition of the air intake roofs and of the air exhaust roofs within the chute is of great importance e.g. for the evenness of the drying result, and in particular for the energy consumption associated therewith and for the drying time, it was already attempted in the past to optimize this arrangement, wherein the particular roofs are typically disposed in horizontal planes located on top of one another.
Thus, it is also important that the drying chute itself, this means its outer shell, together with the support frame and the installed equipment, like e.g. the air roofs, is comprised of plural modules placed on top of another, mostly made of steel sheet material, stainless steel or aluminum, which are placed on top of another and which can thus be assembled quickly, since the air roofs are already preinstalled in the modules in said locations.
In a first state of the art embodiment, the air roofs are disposed directly below one another in vertical direction, this means not offset relative to one another in the particular planes, so that one plane only includes air intake roofs, and the next plane only includes air exhaust roofs.
The disadvantage of this embodiment is that the bulk material piles up on the particular roofs but runs downward in between rather quickly and that the retained material is either overheated or is not dried or is only dried when the chute is completely emptied, so that an uneven drying result is accomplished.
In a second known embodiment, the air roofs are not disposed directly below one another in vertical direction, but offset relative to another in lateral direction, so that a roof is disposed respectively under the gap between the roofs of the next plane above, this means in a diamond pattern comprising only slanted pattern lines.
Thus, in one plane, only air intake roofs are installed and in the next plane below only air exhaust roofs are installed, etc.
The advantage of this configuration is that the bulk material thus runs from the top to the bottom in particular in meandering material flows, and no retaining zones are formed.
The disadvantage of this configuration is that the air only flows through a vertical partial flow of the bulk material on its path from one air intake roof to the most proximal roof only from one side, which yields uneven drying action of the bulk material within said material air exhaust roof, since the drying effect on the side of the partial flow facing the air intake roof is higher through the air, which is still warm and dry, than on the side of the material flow facing away from the air intake roof and facing the air exhaust roof.
A third known embodiment as described in FIG. 1c avoids said disadvantage by mounting the particular identically configured modules viewed in top view by 180° rotated relative to one another.
When a respective even number of planes is disposed within the modules, this induces the flow direction of a partial material flow to remain constant within a module, however, the flow direction of the partial flow to change from one side to the other at the transition from one module to the next.
The disadvantage of this solution is that an accumulation of air exhaust roofs or air intake roofs occurs at each separation plane between two modules, since the two adjacent roof modules respectively comprise the same type of roofs above and below the horizontal joint between two modules, while the type of roofs changes respectively from the top to the bottom, thus in the sequence of the planes in the interior of a module.
This leads to an uneven airflow in the boundary portion between two modules, which is greatly reduced compared to the desired medium air velocity in a boundary portion, and greatly increased in the other one.
The increased air velocity thus would lead to an increased removal of small and light components of the bulk material, in case of grain e.g. broken kernels, in case of canola e.g. canola seeds, which typically constitutes an undesirable loss of mass, so that for this reason the overall set velocity of the intake air and of the exhaust air has to be reduced.
In order to arrive at the same drying result, thus the size, in particular the diameter, of the chute has to be increased, which increases cost.